Validate uniqness in child collection

Hi, All. I have a class with some property of type collection strings. For example,

public class TestClass
{
    public List<InnerCollection> Collection { get; set; }
}

public class InnerCollection
{
    public string Name { get; set; }
}

RuleForEach(x => x.Collection)
        .Must((parent, col) => parent.Collection.GroupBy(x => x.Name).Count() > 1 })
        .WithMessage("The {0} symbol already exists.",
        (parent, col) => col.Name);

Can I create validation rule that returned for me only ONE validation message?

[JeremySkinner]

You’d need to write a custom validator to manually handle the logic for that, which then concatenates the failed items together into a single message. Something like this should work:

public class UniqueInnerCollectionValidator : PropertyValidator {
    public UniqueInnerCollectionValidator() 
        : base("The following symbols already exist: {symbols}") {

    }

    protected override bool IsValid(PropertyValidatorContext context) {
        var listOfCollection = context.PropertyValue as List<InnerCollection>;
        if (listOfCollection == null) {
            return true;
        }

        var nonUniqueKeys = listOfCollection.GroupBy(x => x.Name).Where(x => x.Count() > 1).Select(x => x.Key).ToList();

        if (nonUniqueKeys.Count > 0) {
            string failedItems = string.Join(", ", nonUniqueKeys.ToArray());
            context.MessageFormatter.AppendArgument("symbols", failedItems);
            return false;
        }

        return true;
    }
}

…useable like this:

RuleFor(x => x.Collection).SetValidator(new UniqueInnerCollectionValidator());

The error message contains all the names that caused failures concatenated together.

[JeremySkinner]

No, sorry - AddRule basically completely bypasses the standard fluent interface and allows you to write your own rules, so you’d have to also include any other validation (null checks etc) inside the delegate.